The invention relates to a polyesters, and more particularly of polyesters derived from cycloaliphatic diols and cycloaliphatic esters and a process for their formation.
Poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate), PCCD, is a known polyester referred to in U.S. Pat. No. 2,891,930 to Caldwell et al and U.S. Pat. No. 2,901,466 to Kibler et al. Kibler et al discusses poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) as one of the sixty-eight examples of linear polyesters and polyesteramides. According to Example 42, an excess amount of the glycol or 1,4-cyclohexanedimethanol component is utilized for making poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate). U.S. Pat. No. 4,327,206 to Winston et al describes the reaction of 1,4-cyclohexanedicarboxylate with aromatic diols.
U.S. Pat. No. 5,986,040 to Patel and Smith describes the production of PCCD having a melting point of the final moldable linear PCCD from 208 to 224 degrees as shown in Table 3 of the Examples.
Typically, molding compositions based upon blends of thermoplastic resin incorporating 1,4-cyclohexanedicarboxylic acid residues in the polymer chain may have good impact resistance, good processability, and transparency. U.S. Pat. No. 5,986,040 to Patel and Smith describes PCCD resins having those properties. Further and additional improvements to the properties, such as thermal capacity, are desirable.
The present invention is directed to an improved process for producing a moldable linear poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate), PCCD, resin having crystalline properties with an enhanced melting temperature that makes it suitable for polymer blends. By the improved process, the melting points of the PCCD is enhanced to about 225 to about 234 degrees Centigrade thereby improving the thermal capability and crystallinity of the resin.
Typically, the crystallinity of PCCD, is not as high as that of such commercially available polyesters as poly(1,4-butylene terephthalate), or xe2x80x9cPBTxe2x80x9d which is an ingredient of many resin blends, such as blends with polycarbonate and other thermoplastic polymers. In addition to imparting desirable molding characteristics, enhanced crystallinity imparts such advantageous properties as its resistance to solvents. Thus, it is desirable to enhance the crystallinity of poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) and produce a poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) with uniform melting properties which permit its incorporation into thermoplastic blends useful for weatherable molding type applications. Enhanced crystallinity results in a desirable higher melting temperature for a given degree of polymer polymerization.
For sake of clarity, the following Table 1 sets forth the meaning of the abbreviations used throughout the specification.
A linear cycloaliphatic polyester resin consists essentially of a polyester having the formula: 
where R is an alkyl from 1 to 6 carbon atoms or residual endgroups derived from either monomer, and n is greater than about 70. The polyester is derived from the transesterification reaction of a starting DMCD and a starting CHDM.
DMCD and CHDM are polymerized to produce a low viscosity polymer intermediate PCCD with a melt viscosity of from about 50 to about 800 poise, preferably from about 200 to about 500 poise.
Next, the low viscosity intermediate is solid state polymerized at a temperature from about 175 C to about 210 C, preferably from about 190 C to about 206 C, to produce a resulting PCCD polymer having a melting temperature, Tm, about 225 to about 234 degrees Centigrade having improved thermal capability due enhanced crystallinity of the resin.
The preferred enhanced melt viscosity of the final prepared PCCD is from about 2,000 to about 22,000 poise. For applications for extruding the resulting resin into a sheet form, the preferred melt viscosity is from about 7000 poise to about 22000 poise, and more preferably from about 10000 poise to about 18000 poise. For application for injection molding the resulting resin, the preferred melt viscosity is from about 1000 poise to about 10000 poise and more preferably from about 2000 to about 6000.
The starting CHDM and DMCD are reacted in the presence of a catalyst in an inert atmosphere to form the low viscosity PCCD polymer having ester end groups such as a carboxycyclohexanecarboxylate end group (or ester thereof) and acid or hydroxy end groups such as alkyoxycyclohexanealkyanol end groups. The low viscosity intermediate preferably has hydroxy end group to ester end group present in about a 1 to 1 ratio so that molecular weight may be increased by further polymerization of the oligomer. The intermediate is next further reacted for increasing the molecular weight of the PCCD. For the intermediate oligomer, the acid number which is determined by the number of acid end groups on the polymer chain is preferably less than about 10, preferable less than 6 meq/kg as determined from the titration method. Preferably the amount of catalyst present is less than about 200 ppm. Typically, catalyst may be present in a range from about 20 to about 300 ppm.
The starting CHDM has a trans-CHDM greater than the equilibrium amount and the reaction is carried out in an inert atmosphere under conditions to minimize trans to cis isomerization of said starting DMCD. These conditions require the starting DMCD and the starting CHDM to be present in a molar stoichiometric amount to a slight molar excess of DMCD so that the number of ester end groups such as acid or methyl carboxycyclohexanecarboxylate end groups and the number hydroxy end groups such as alkyoxycyclohexanealkyanol end groups are in substantially equal proportions for the low viscosity PCCD intermediate. The resulting low viscosity PCCD is then reacted to build molecular weight.
Also, in accordance with preferred conditions for preparing the PCCD oligomer, it is desirable to minimize the time period for forming the PCCD oligomer to prevent trans-to-cis isomerization. The utilization of a stoichiometric excess of diol or CHDM as a starting reactant slows the reaction rate and results in undesirable isomerization of DMCD. A slight stoichiometric excess of ester or DMCD is preferred to compensate for material imbalance created during the process, thereby enhancing the polymerization rate. Preferred starting temperatures of the reaction are from about 120 to about 140 degrees Centigrade. The preferred order for adding reactants comprises charging the CHDM to the reaction vessel or container, adding the DMCD in slight stoichiometric excess, and, next, adding the catalyst to the reaction vessel containing the starting reactants at the initial reaction temperature. This step is preferably conducted under an inert atmosphere, such as nitrogen, to form a distillate which is typically collected by condensation. The distillate by-product is, based on the starting material, typically an aliphatic alcohol, such as an alkyl alcohol of 1 to 12 carbon atoms. When CHDM is reacted with DMCD, methanol is removed during the ester interchange reaction as the reaction mixture is heated from the starting temperature to about 200 to about 250, preferably from 220 to 240 degrees Centigrade.
The PCCD acid interchange oligomer formed is further reacted to form a suitable low viscosity PCCD intermediate polymer that may be solid state polymerized to form a PCCD product that is suitable for use in polymer blends. The low viscosity PCCD intermediate is formed by increasing the molecular weight of the acid interchange oligomer under conditions of less than atmospheric pressure for removing distillate by-product. In the melt polycondensation stage for producing the intermediate oligomer, the temperature of the reaction mixture containing oligomers is increased to about 230 to 270 Centigrade, preferable from 250 to 265 degrees Centigrade. After a reaction time on the order about 15 minutes to about 40 minutes the reaction is halted to produce the low viscosity PCCD polymer having low viscosity from about 50 to about 800 poise. The low viscosity intermediate is preferably removed from reactor. Solid resin chips are then further polymerized in the solid state. For solid state polymerization, the polycondensation reaction is most preferably carried at a temperature of about 206 degrees Centigrade to obtain the PCCD having the desired melting temperature and viscosity has previously described.
PCCD is an aliphatic polyester resin which has desirable properties for weatherable applications. The polyester is made by reacting dimethyl 1,4-cyclohexanedicarboxylate (DMCD) with 1,4-cyclohexanedimethanol (CHDM) in the presence of a catalyst (e.g. TPT). Preferably, control of stoichiometry during the formation of the oligomer intermediate is critical while minimizing isomerization of DMCD from trans to cis isomer.
Melt polymerization of 1,4-cyclohexanedimethanol (CHDM) and dimethyl trans-1,4-cyclohexanedicarboxylate (t-DMCD) in the presence of a catalyst such as titanium(IV) isopropoxide (TPT) results in the polyester resin PCCD: 
PCCD is an aliphatic polyester resin made from CHDM (diol), and t-DMCD (diester). In the present invention, n is preferably greater than about 70 and preferably from about 70 to about 150. R is an alkyl group of 1 to 6 carbon atoms. Preferably R is methyl or ethyl and most preferably methyl. The end groups consist essentially of 4-carboxycyclohexanecarboxylate group having the formula 
and 4-methanolcyclohexanemethylene group having the formula 
Preferably the end groups are present in substantially equal proportions. The PCCD of the present invention is characterized by a relatively low acid content.
Both monomers are hydrogenation products of DMT as set forth in the example below wherein hydrogenation of the aromatic ring leads to two geometric isomers, the trans and cis isomers for each monomer. 
The monomers have the following formulation. 
European 0 353 990 B1 (1994) to Y. Tateno describes a process to produce trans-enriched CHDM by selective distillation of trans-CHDM from cis/trans CHDM mixtures heated in the presence of base. CHDM is supplied with xcx9c70-72% trans content, slightly below the thermodynamic equilibrium trans:cis ratio (xcx9c76% trans isomer). DMCD is available with  greater than 95% trans content. The thermodynamidc equilibrium for DMCD is at xcx9c66% trans content. It is preferable to have trans-enriched CHDM and DMCD as starting components above the thermodynamidc equilibrium.
Upon hydrogenation of DMT, the two geometric isomers of CHDM and DMCD are obtained. When the starting DMCD comprises greater than about 90 percent trans content, the final FCCD comprises repeating units derived from DMCD having greater than about 85 percent trans content and preferably greater than about 90 percent trans content. Preferably, less than about 10 percent, more preferably less than about 5 percent of the DMCD undergoes isomerization.
The isomerization of DMCD is Lewis-acid (e.g. TPT) catalyzed and can occur during polymerization: 
The trans:cis ratios are important since the Tm of the polymer is related to the frans:cis ratio. According to the present invention, the rate of isomerization vs. polymerization is an important parameter that is desirably controlled during the process for the formation of PCCD.
According to the present invention, when making PCCD polyester by a melt polymerization process, it is desirable to adjust the process parameters to obtain a predetermined and optimized melt viscosity and melting point Tm. The reaction rate and the mass balance of the PCCD polymerization reaction are desirably controlled so as to reduce variability of the maximum melt viscosity and reduce polymer Tm variability.
TGA results show that DMCD begins to vaporize at around 125xc2x0 C., whereas CHDM begins to vaporize at 180xc2x0 C. The variability in Tm is due to trans to cis isomerization of the DMCD portions of the polymer backbone, which can be affected by longer reaction times. Higher trans content results in a higher Tm, higher degree of crystallinity, and faster crystallization rates.
Preferred reactor starting temperature was lowered to 130xc2x0 C. CHDM was charged before t-DMCD. The vacuum rates for the polycondensation stage was ramped from an initial state to a higher vacuum. The stoichiometry was set at 1.005:1 diester:diol.
Table 2 below shows some properties of the PCCD polymer as a function of different melt viscosities and Tm""s.
The two most critical factors governing PCCD polymerization and the resulting polymer properties (e.g. Tm) were found to be: 1) control of stoichiometry prior to charging the reactor and in the reactor during the polymerization, and 2) control of trans to cis isomerization of DMCD during the polymerization.
The rates of transesterification reactions will depend on the sterics and electronics of the endgroups. Cyclohexyl endgroups are very bulky, especially compared to the hydroxybutyl endgroups found in PBT. For commercially produced polyesters such as poly(ethylene terephthalate), PET, and poly(butylene terephthalate), PBT, high diol:diester ratios are preferred because they enhance oligomer formation rates without inhibiting polycondensation rates. For PCCD, however, high glycol to diester monomer ratios lead to very slow polycondensation rates and an undesirable decrease in trans-DMCD content.
Therefore, proper measurement and addition of monomers when charging a reactor is critically important. In addition, side reactions, physical properties, and chemical properties of the monomers can significantly influence the degree to which the polymer builds molecular weight. For PCCD, side reactions do not appear to influence the degree of polymerization. The stoichiometry and the physical properties of the monomers, on the other hand, have turned out to be critically important.
The variability in melting point is attributed to the trans isomer content of the CHDM and DMCD moieties in the polymer. Although CHDM does not isomerize during the polymerization, its initial trans content still effects the final melting temperature of the polymer. In contrast, DMCD does show trans to cis isomerization during the polymerization process, in spite of its high initial trans content. The trans:cis ratios may be determined by C-13 NMR, and can be determined using a 300 MHz FT-NMR spectrometer.
Although the PCCD process is nominally run in an EI stage followed by a polycondensation stage, the polycondensation transesterification rates for PCCD appear to be extremely slow. The glycol component in PCCD is CHDM, which has two characteristics that make the polycondensation reaction difficult. First, CHDM has low volatility, making it difficult to remove from the system. Second, CHDM is very bulky and creates a large amount of steric hindrance that inhibits transesterification once the CHDM is attached to a t-DMCD carboxyl group. In other words, CHDM endgroups act like chain-stoppers due to slow transesterification kinetics. Therefore, in order to obtain high molecular weight PCCD, the ester interchange reactions are critical to building molecular weight. The result is that a stoichiometrically controlled ratio of diester to diol is required in order to obtain equal numbers of hydroxyl and ester endgroups and maximize build through ester interchange.
The preferred ratio of diester:diol (DMCD:CHDM) is 0.98 to 1.02; more preferred is 0.995 to 1.005. It is contemplated that a slight excess of diester DMCD may be added to compensate for volatility of DMCD during the reaction. Typically, such excess of DMCD utilized is less than one percent but the excess may vary from reactor to reactor.